The present invention relates to a sliding bearing comprising a back metal and a bearing alloy layer bonded thereto, and more particularly to a sliding bearing with improved conformability.
In gasoline and Diesel engines, for instance, as a main bearing for supporting a crankshaft thereof, two half sliding bearings are combined together and used, each half sliding bearing comprising a steel back metal and a bearing alloy layer of Cu- or Al-based alloy formed on the back metal and, if necessary, an overlay formed on the surface of the bearing alloy layer. Incidentally, in the above-described bearings for engines, it is general that an overall thickness is about 1.5 mm, a thickness of the back metal is about 1.2 mm, a thickness of the bearing alloy layer is about 0.3 mm, and a thickness of the overlay formed as the occasion demands is about 20 .mu.m.
FIG. 5 is an axial sectional view of a main sliding bearing showing axial distributions of oil film pressure. In a steady state achieved after the main sliding bearing and a crankshaft had come to have conformability, the pressure on the oil film occurring between a bearing alloy layer (or an overlay) and the crankshaft is high at the axially middle portion and becomes lower gradually toward each axial end, as shown by a solid line in FIG. 5. However, in an initial state before they have come to have satisfactory conformability, the pressure on the oil film is higher at each axial end portion than at the middle portion, as shown by a broken line in FIG. 5.
One of reasons for high oil film pressure at each axial end portion is the misalignment between the crankshaft and such each axial end portion in the initial state. In other words, If misalignment or the like takes place, the thickness of the oil film becomes smaller and accordingly the pressure on the oil film becomes higher at such each axial end portion. In this way, at each axial end portion, the oil film thickness becomes thin and the oil film pressure becomes high. Such thin oil film is liable to be ruptured due to fluctuations in load and rotational speed and so on. If the oil film is ruptured, there will be caused what is called metallic contact that the crankshaft and the bearing alloy layer (or overlay) are brought into direct contact with each other, resulting in wear of the bearing alloy layer. After the opposite end portions of the bearing alloy layer have been worn out at an early state in the manner described above, loads must be borne by portions subtracting the opposite end portions, with the result that a pressure receiving area is reduced to shorten the service life of the bearing.